The present invention relates to an actuator that applies a driving force to a movable part axially supported on a torsion bar, to drive the movable part, and in particular to an actuator of a construction ideally suitable to an actuator equipped with a mirror portion for optical scanning.
Through the development of micro-electronics, represented by the high integration of semiconductor devices, many devices have undergone considerable miniaturization together with increases in functionality. In recent years, there have been utilized in laser optical scanning systems and the like, micro-miniature semiconductor actuators using semiconductor manufacturing technology.
Conventionally, these types of micro-miniature semiconductor actuators have been produced in the manner described below.
Using semiconductor manufacturing processes, a movable part equipped with a mirror for scanning light on the surface of a semiconductor substrate, and a beam portion axially supporting the movable part, are integrally formed on a silicon substrate. This silicon substrate with the movable part and the beam portion is then arranged on a glass substrate. At this time, the arrangement is made such that the center of the movable part is in contact with a projection on the glass substrate, and due to an indentation in the glass substrate, a fixed gap exists between the movable part and the glass substrate. Furthermore, a pair of electrodes for rotating and driving the movable part is provided on either side of the glass substrate projection.
In a semiconductor actuator of such a structure, by applying an external voltage between one of the electrodes and the movable part, an electrostatic attraction acts on the movable part, thus tilting the movable part. By applying a voltage alternately to each of the pair of electrodes, the movable part is driven to swing, so that reflected light from the mirror on the surface of the movable part is scanned.
However in the conventional semiconductor actuators of this type, since the movable part is extremely thin, when driving the movable part, the edge of the movable part is warped in the opposite direction to the rotation direction or the same direction of the rotation direction, due to air resistance, moment of inertia and the driving force acting on the edge of the movable part. Furthermore, in the conventional semiconductor actuator, since the movable part is a planar rectangular shape simply cut out of a silicon substrate, the affect of the warped edge is transmitted to the central portion of the movable part, causing a warp also in the central portion. As a result, in the case in which the mirror is positioned in the central portion of the movable part, the mirror is warped, interfering with the scanning of the reflected light from the mirror surface.
Moreover, in a semiconductor actuator of a structure in which a drive coil for generating a magnetic field by the electric current supply is provided on the movable part, and a static magnetic field acts on the drive coil to thereby generate a Lorentz force for driving the movable part, heat is generated in the drive coil as a result of the electric current supply. Therefore, in addition to the warp described above, the movable part is warped due to a bimetal action caused by a difference in the coefficient of thermal expansion of the mirror material and that of the substrate material. Furthermore, for the purpose of protecting and insulating the drive coil, the drive coil is covered with a protective film of polyimide or the like, but this protective coat also causes a warp of the movable part due to residual compressive stress within the protective coat.
In this manner, conventional semiconductor actuators are prone to deformation problems of the central portion of the movable part resulting from the influence of air resistance, moment of inertia, heat and residual compressive stress. In particular, when a mirror is provided on this central portion of the movable part, the warp results in interference with the optical scanning function.
The present invention addresses the problems outlined above, with an object of providing an actuator of a construction capable of suppressing deformation of the central portion of the movable part.
To achieve the above object, the present invention provides an actuator comprising a movable part and a torsion bar for axially supporting the movable part in a rotatable manner, the movable part being applied with a driving force to be driven, wherein a boundary portion for suppressing causes of deformation of a central portion of the movable part, which are transmitted from an edge of the movable part to the central portion of the movable part, is provided between the central portion of the movable part and at least an edge of the movable part parallel with the torsion bar.
With such a construction, by essentially separating the edge of the movable part and the central portion of the movable part with the boundary portion, causes of deformation from the edge of the movable part are less likely to be transmitted to the central portion of the movable part.
According to a second aspect of the invention, the construction may be such that the movable part is provided with a mirror portion on the central portion thereof and a driving force generating portion on the edge thereof. Then, by substantially separating the driving force generating portion on the edge of the movable part from the mirror portion on the central portion of the movable part with the boundary portion, it is difficult for causes of deformation from the driving force generating portion on the edge of the movable part, to be transmitted to the mirror portion of the movable part central portion, and hence deformation of the mirror portion can be suppressed.
According to a third aspect of the invention, the construction may be such that the mirror portion and the driving force generating portion are provided on the same face of the movable part. Or, according to a fourth aspect of the invention, the construction may be such that the driving force generating portions are provided on both front and rear faces of the movable part. If the driving force generating portions are provided on both the front and rear faces of the movable part, then compared with the case where the driving force generating portion is provided on only one of the front or rear faces of the movable part, the rotation angle of the movable part can be increased in case of the same electric current supply amount, and further the electric current supply amount can be reduced in case of the same rotation angle.
According to a fifth aspect of the invention, the driving force generating portion may be a coil portion provided on the periphery of the movable part for generating a magnetic field by the electric current supply, the construction being such that a static magnetic field acts on the coil portion on the edge of the movable part to generate the driving force and drive the movable part. Moreover, according to a sixth aspect of the invention, the driving force generating portion may be a thin film magnet provided on the periphery of the movable part, the construction being such that an electromagnetic attraction acts on the thin film magnet to drive the movable part.
The boundary portion may be a through hole according to a seventh aspect of the invention. In this situation, according to an eighth aspect of the invention, the through hole may be provided around the whole periphery of the central portion or mirror portion, while remaining a part of the movable part between the edge of the movable part and the central portion of the movable part. Then, the region of the through hole for suppressing transmission of causes of deformation from the edge of the movable part to the central portion can be extended. Furthermore, the driving force is transmitted to the movable part central portion via the remaining movable part between the edge of the movable part and the movable part central portion so as to be able to rotate the movable part. Also, according to a ninth aspect of the invention, the construction may be such that a filler which can suppress the causes of deformation and which is made of a material different to a material of the movable part is filled into the through hole.
According to a tenth aspect of the invention, the boundary portion may be a groove. In this case, the groove may be formed in either one of the front and rear faces of the movable part according to an eleventh aspect of the invention, or this may be formed in both the front and rear faces according to a twelfth aspect of the invention. Moreover, according to a thirteenth aspect of the invention, the groove may be formed around the whole periphery of the central portion or the mirror portion. Further, according to a fourteenth aspect of the invention, the construction may be such that the groove is filled with a filler which can suppress the causes of deformation and which is made of a material different to a material of the movable part.
According to a fifteenth aspect of the invention, the boundary portion may be formed from a filler which can suppress the causes of deformation and which is made from a material different to a material of the movable part. In this case, according to a sixteenth aspect of the invention, the filler may be provided around the whole periphery of the central portion or the mirror portion.
Moreover, the present invention provides an actuator comprising a movable part and a torsion bar for axially supporting the movable part in a rotatable manner, the movable part provided with a mirror portion for reflecting a light beam and a driving force generating portion that applies a driving force on the movable part, so that the movable part is driven by the driving force, wherein a boundary portion for suppressing causes of deformation of the mirror portion, which are transmitted from the driving force generating portion to the mirror portion, is provided between the mirror portion and driving force generating portion of the movable part.
With such a construction, the boundary portion substantially separates between the mirror portion and the driving force generating portion, thus the causes of deformation from the driving force generating portion are less likely to be transmitted to the mirror portion.